The primary goals of the proposed research is to determine the role of glucocorticoid receptor (GR) in multistage mouse skin carcinogenesis. Earlier work from our laboratory as well as others has shown that glucocorticoid hormones are very potent inhibitors of DNA synthesis in normal keratinocytes but transformed keratinocytes become resistant to the growth inhibition by glucocorticoids as well as to other effects of these hormones. Additional studies from our laboratory showed that in spite of the resistance to glucocorticoids, GR levels and GR gene structure are not changed in transformed keratinocytes, suggesting that an alteration of GR function rather than expression plays an important role in mouse skin carcinogenesis. Current evidence indicates that protein p65 from the NF-kappaB family of transcription factors interacts with GR at a protein-protein level and plays a role as a dominant negative inhibitor of GR function. Recently we discovered that p65 is overexpressed in mouse skin tumors and transformed keratinocyte cell lines. We propose to test the hypothesis that alteration of GR function is a critical event during the tumor promotion stage that allows uncontrolled growth of transformed keratinocytes. In addition, this project entails analysis of p65 as a dominant negative inhibitor of GR in keratinocytes. In addition, this project entails analysis of p65 as a dominant negative inhibitor of GR in keratinocytes. The Specific Aims are: 1) To further examine the sequential changes of GR function in skin carcinogenesis; 2) To determine the sequential changes in the expression of NF-kappaB and IkappaB proteins during multistage carcinogenesis; 3) To examine the effect of NF-kappaB protein p65 on GR function and glucocorticoid-responsiveness in keratinocytes; 4) To develop transgenic animals deficient in the GR expression of overexpressing GR in epidermis to address the tumor suppressor role of GR in skin carcinogenesis; 5) To develop transgenic mice that overexpress NF-kappaB protein p65 to further study p65/GR interaction in multistage skin carcinogenesis.